University Of Quebec: Night Work And The Risk Of Cancer In Men

"Reduction in melatonin may allow levels of hormones to increase over an extended period..."

This research examined possible connections between extended night work and cancer rates in men. This research indicated some correlation between long periods of working through the middle of the night and subsequent development of cancers at certain sites in the body. 

It is theorised that exposure to light at night-time disrupts the production of melatonin, which normally regulates the circadian rhythm and reproductive hormone levels. Through its supression, this reduction in melatonin may allow levels of hormones to increase over an extended period and it is thought that this increased level may contribute to specific male cancers.

Past research has shown some connections between breast cancer in women and long periods of working at night. The International Agency For Research On Cancer  has designated shift work that involves circadian disruption as a likely contributor to cancer development.

Cancers That Were Noted To Increase Through Night Work

There were elevated levels of bladder, prostate and colon cancer and non-Hodgkins lymphoma but other cancer sites did not see an increase. For employers managing the health and wellbeing of staff, this research may influence the way that shifts are arranged.